1. Field of the Invention
This invention relates generally to air cannons of the type used for removing bulk material deposits from the walls of industrial vessels and other bulk material handling devices, such as kilns used in the cement and paper industries. More particularly, the present invention pertains to an automated blast guard valve, downstream of the air cannon's discharge valve, that opens before each firing of the air cannon and that closes thereafter.
2. General Background
Air cannons are commonly used for removing the buildup of bulk material deposits on the walls of bulk material handling devices, such as kilns and hoppers. An air cannon generally comprises a pressure vessel and a discharge valve. When the discharge valve is actuated, pressurized gas within the pressure vessel escapes therefrom and blasts against the accumulated bulk material, thereby dislodging the accumulated bulk material from surfaces of the bulk material handling device. Although the compressed gas is typically air, other gases such as nitrogen or carbon-dioxide is also sometimes used. Regardless of the composition of the gas, the device itself is commonly and herein referred to as an air cannon.
Periodically, some bulk material handling devices require internal maintenance. When such maintenance occurs, the inadvertent firing of an air cannon can cause potential harm to maintenance workers. As such, some air cannon assemblies incorporate a blast guard valve operatively between the discharge valve of the air cannon and the bulk material handling device to which the air cannon is attached. A blast guard valve allows a maintenance worker to manually obstruct the gas passageway that connects the air cannon to the bulk material handling device. A blast guard valve also prevents bulk material from traveling from the bulk material handling device to the discharge valve of the air cannon during the maintenance of the bulk material handling device. This potentially prevents the bulk material from obstructing the discharge valve when operation of the air cannon resumes. More significantly, when a blast guard valve is closed such that it obstructs the gas passageway, the blast guard valve prevents the pressurized gas from blasting into the bulk material handling if the air cannon's discharge valve inadvertently fires, and thereby provides an additional level of protection for the maintenance workers. When maintenance is complete, the blast guard valves can be reopened so that the normal operation of the air cannons can resume.
The normal operating conditions within a bulk material handling device can be very harsh. For example, kilns can contain very hot bulk material that is also abrasive and corrosive. Unfortunately, the blast guard valves are often exposed to such bulk material during the normal operation of the bulk material handling devices. Over time, this exposure has the tendency to seize or block the blast guard valves in a manner making it difficult or impossible to later close the blast guard valves prior to servicing the bulk material handling devices. As a result, there is a potential that some of blast guard valves will be left open during the maintenance of the bulk material handling devices.